Tetrahydrofuran → 3-Diphenylmethoxycarbonyl-1-(2-benzyloxycarbonylamino-4-thiazolyl)-2-propene-1,1-dicarboxylic acid diethyl ester

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To a solution of 2-(2-benzyloxycarbonylamino-4-thiazolyl)malonic acid diethyl ester in tetrahydrofuran (20 parts) are added sodium hydride (2.35 equivalents) and a solution of trans-3-chloroacrylic acid diphemylmethyl ester (1.2 equivalents) in tetrahydrofuran (8 parts) under ice cooling. After stirring at 35° to 40° C. for 12.5 hours, the mixture is diluted with ethyl acetate and diluted hydrochloric acid, washed with water, dried, and concentrated. The residue is chromatographed over silica gel. The fraction eluted with a mixture of benzene and ethyl acetate (15:1) is crystallized from ethyl acetate to give 3-diphenylmethoxycarbonyl-1-(2-benzyloxycarbonylamino-4-thiazolyl)-2-propene-1,1-dicarboxylic acid diethyl ester.

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